1. Profilometer
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A profilometer is a measuring instrument used to measure a feature's length or depth,
usually in the micrometre or nanometre level.
While the historical notion of a profilometer was a device similar to a phonograph that
measures a surface as the surface is moved relative to the contact profilometer's stylus,
this notion is changing along with the emergence of numerous non-contact profilometery
techniques.
[edit] Contact profilometers:
A diamond stylus is moved vertically in contact with a sample and then moved laterally
across the sample for a specified distance and specified contact force. A profilometer can
measure small surface variations in vertical stylus displacement as a function of position.
A typical profilometer can measure small vertical features ranging in height from 10 to
65,000 nanometres. The height position of the diamond stylus generates an analog signal
which is converted into a digital signal stored, analyzed and displayed. The radius of
diamond stylus ranges from 5 μm to about 25 μm, and the horizontal resolution is
controlled by the scan speed and scan length. There is a horizontal broadening factor
which is a function of stylus radius and of step height. This broadening factor is added to
the horizontal dimensions of the steps. The stylus tracking force is factory-set to an
equivalent of 50 milligrams (~500 mN).
Advantages of contact profilometers:
• Acceptance: Most of the world's surface finish standards are written for contact
profilometers. To follow the prescribed methodology, this type of profilometer is
often required.
• Surface Independence: Due to the fact that the stylus is in contact with the
surface, this method is not sensitive to surface reflectance or color. Also,
contacting the surface is often an advantage in dirty environments where non-
contact methods can end up measuring surface contaminants instead of the
surface itself.
[edit] Non-contact profilometers:
An optical profilometer is a non-contact method for providing much of the same
information as a stylus based profilometer. There are many different techniques which
are currently being employed, such as laser triangulation (triangulation sensor), confocal

2. microscopy and digital holography.
Advantages of optical profilometers:
• Speed: Because the non-contact profilometer does not touch the surface the scan
speeds are dictated by the light reflected from the surface and the speed of the
acquisition electronics.
• Reliability: Optical profilometers do not touch the surface and therefore cannot be
damaged by surface wear or careless operators. Many non-contact profilometers
are solid-state which tends to reduce the required maintenance significantly.
• Spot size: The spot size, or lateral resolution, of optical methods ranges from a
few micrometres down to sub micrometre. On the small end, this is roughly an
order of magnitude smaller than typical stylus tips.
One special application is road pavement profilometers. These are of non-contact type,
most of them use laser triangulation in combination with an inertial unit that establishes a
large reference plane to which the laser readings are related. The inertial compensation
makes the profile data more or less independant of what speed the profilometer vehicle
had during the measurements.

3. Method of thin film process control and calibration standard for optical
profilometry step height measurement
Document Type and Number:
United States Patent 6490033
Link to this page:
http://www.freepatentsonline.com/6490033.html
Abstract:
A method of calibrating an interferometer system and a multilayer thin film used for
calibrating the interferometer system. The method including measuring the step height of
a gold step with the interferometer system, the multilayer thin film comprising a gold
layer that defines the gold step. The multilayer thin film having an optical flat, a first
layer on the surface of the optical flat, a second layer on the first layer, a test layer on a
part of the second layer, and a gold layer on the test layer and on a part of the second
layer uncovered by the test layer. The test layer having a test layer step, and the gold
layer having a gold step over the test layer step. Also, a reference standard and a method
of making the reference standard for a thin film sample with one or more component
thin film layers, the reference standard having a gold layer over the surface of the thin
film sample.
1. A method of calibrating an interferometer system comprising: measuring the height of
a gold step with the interferometer system, the gold step being in a gold layer of a
multilayer thin film for use as a calibration standard, the multilayer thin film
comprising:
an optical flat;
a first layer on the surface of the optical flat;
a second layer on the first layer, the second layer having a first part and a second part;
a test layer on the first part of the second layer, the test layer having a test layer step; and,
a gold layer on the test layer and on the second part of the second layer, such that the gold
layer has said gold step over said test layer step.
2. The method of claim 1 wherein the first layer has a thickness of 50 nm or less, the
second layer has a thickness of 50 nm or less, and the gold layer has a thickness between
15nm and 65 nm.
3. The method of claim 2 wherein the first layer has a thickness of about 30 nm or less,
the second layer has a thickness of about 30 nm or less, and the gold layer has a thickness
between about 30 nm and about 50 nm.
4. The method of claim 3 wherein the optical flat has a .lambda./20 smooth surface of
amorphous material.

4. 5. The method of claim 1 wherein the first layer is titanium with a thickness of about 20
nm, the second layer is platinum with a thickness of about 20 nm, the test layer is
platinum with a thickness of about 6 nm, and the gold layer has a thickness of about 50
nm.
6. The method of claim 5 wherein the optical flat has a .lambda./20 smooth surface of
amorphous material.
7. The method of claim 1 wherein two or more measurements of the step height of the
calibration standard are taken with the interferometer system for calibrating the
interferometer system.
8. A multilayer thin film for use in calibrating an interferometer system comprising:
a. a first layer on the surface of an optical flat;
b. a second layer on the first layer, the second layer having a first part and a second part;
c. a test layer on the first part of the second layer, the test layer having a step; and,
d. a layer of gold on the test layer and on the second part of the second layer, so that the
layer of gold has a step over the step in the test layer.
9. The multilayer thin film of claim 8 wherein the first layer has a thickness of 50 nm or
less, the second layer has a thickness of 50 nm or less, and the gold layer has a thickness
between 15 nm and 65 nm.
10. The multilayer thin film of claim 9 wherein the first layer has a thickness of about 30
nm or less, the second layer has a thickness of about 30 nm or less, and the gold layer has
a thickness between about 30 nm and about 50 nm.
11. The multilayer thin film of claim 10 wherein the optical flat has a .lambda./20
smooth surface of amorphous material.
12. The multilayer thin film of claim 8 wherein the first layer is titanium with a thickness
of about 20 nm, the second layer is platinum with a thickness of about 20 nm, the test
layer is platinum with a thickness of about 6 nm, and the gold layer has a thickness of
about 50 nm.
13. The multilayer thin film of claim 12 wherein the optical flat has a .lambda./20
smooth surface of amorphous material.
14. A method of making a multilayer thin film for use in calibrating an interferometer
system comprising:

5. a. depositing a first layer on the surface of an optical flat;
b. depositing a second layer on the first layer, the second layer having a first part and a
second part;
c. depositing a test layer on the first part of the second layer, the second layer having a
step; and,
d. depositing a layer of gold on the test layer and on the second part of the second layer,
so that the layer of gold has a step over the step in the test layer.
15. The method of claim 14 wherein the first layer has a thickness of 50 nm or less, the
second layer has a thickness of 50 nm or less, and the gold layer has a thickness between
15 nm and 65 nm.
16. The method of claim 15 wherein the first layer has a thickness of about 30 nm or less,
the second layer has a thickness of about 30 nm or less, and the gold layer has a thickness
between about 30 nm and about 50 nm.
17. The method of claim 16 wherein the optical flat has a .lambda./20 smooth surface of
amorphous material.
18. The method of claim 14 wherein the first layer is titanium with a thickness of about
20 nm, the second layer is platinum with a thickness of about 20 nm, the test layer is
platinum with a thickness of about 6 nm, and the gold layer has a thickness of about 50
nm.
19. The method of claim 18 wherein the optical flat has a .lambda./20 smooth surface of
amorphous material.
20. A method of making a reference standard for a thin film sample with one or more
component thin film layers, the thin film sample having a surface, the surface defining a
step with a step height, the method comprising depositing a layer of gold on the surface
of the thin film sample.
21. The method of claim 20 wherein the gold layer has a thickness between about 30 nm
and about 50 nm.
22. The method of claim 20 wherein two or more measurements are taken with the
interferometer system for obtaining a mean value of the height of the step.
23. A reference standard for use in thin film process control, the standard comprising a
layer of gold deposited on the surface of a thin film sample in manufacture for
measurement by an interferometer system.
24. The reference standard of claim 23 wherein the gold has a thickness between about 30

6. nm and about 50 nm.
Description:
FIELD OF THE INVENTION
The invention relates generally to thin films and the interference microscope and
specifically to techniques for calibrating an optical profilometer and for measuring a
thin film surface profile.
BACKGROUND OF THE INVENTION
Optical profilometry is a non-contact method of measuring the surface characteristics of a
thin film sample in three dimensions. Optical profilometry is often preferred to contact
methods, such as atomic force microscopy and surface contact profilometry, because the
latter are intrinsically less accurate and can destroy features of the sample during
measurement.
An optical profilometer is one type of interference microscope (interferometer). An
interference microscope generally is used either to measure or to visualize the phase
differences between two or more beams of electromagnetic radiation, when directed to a
thin film it measures the surface features of the thin film sample under investigation.
When the microscope measures the phase differences, it generates an interference pattern
which a computer can analyze to derive a surface profile of the sample. The microscope
and computer together comprise an interferometer system.
Several beams of the radiation used to measure surface features of a thin film may
penetrate slightly beneath the surface of the thin film before they are scattered. This
penetration depth changes the distance traveled by a beam and may affect the phase
difference between the beam and another beam with which it interferes, creating noise in
the interference pattern and decreasing the accuracy of the measurement. The noise
becomes more significant when the profilometer is used to measure thin film step
heights that fall below 10 nanometers, because at this height the penetration depth is on
the same order of magnitude as the step height. If radiation with a smaller wavelength
and higher energy is used, the noise becomes even greater because this radiation
penetrates even deeper into the thin film. Moreover, the smaller the wavelength, the
more dramatically a slight difference in the path traveled by the radiation affects the
resulting phase difference as well as the interference pattern.
The penetration depth of the beam introduces additional inaccuracies into the process of
calibrating the optical profilometer, especially when the profilometer must be calibrated
for taking measurements of thin film step heights in the sub-10 nanometer range.
Previously the best technique of calibration for these step heights was to calibrate to a
much higher step and then extrapolate blindly to a step that is an order of magnitude
lower. Alternately, a contacting measuring method might have been used instead of non-
contact optical profilometry.
Unfortunately, the technique of calibrating to a higher step may yield imprecise

7. measurements. Alternately, contacting measuring methods may damage the surface
features of a thin film sample. Further, these methods are generally less accurate and
may be more costly.
Another drawback of measuring a step height with an optical profilometer arises when
the step does not have an identical composition in its upper and next lower levels. In
particular, if the upper level of the step comprises one metal with one penetration depth
while the next lower level comprises a different metal with a different penetration depth,
the step might create even more noise in the interference pattern.
SUMMARY OF THE INVENTION
Accordingly, an object of one embodiment of the invention is to provide a technique for
calibrating an optical profilometer to measure very small step heights. Another object of
an embodiment of the invention is to provide a calibration standard for optical
profilometry step height measurements. Another object of an embodiment of the
invention is to provide a technique for measuring very small step heights. Another object
of an embodiment of the invention is to provide a reference standard for thin film
process control.
Briefly described, and in accordance with one embodiment thereof, the invention
provides a method of calibrating an interferometer system including measuring the step
height of a gold step with the interferometer system. The gold step is in a gold layer of a
multilayer thin film which acts as a calibration standard. The multilayer thin film
(calibration standard) has an optical flat, a first layer on the surface of the optical flat, a
second layer on the first layer, a test layer on a part of the second layer, and a gold layer
on the test layer and on a part of the second layer uncovered by the test layer. The test
layer has a test layer step, and the gold layer has the gold step over the test layer step. The
gold step is equivalent in height to the test layer step and exhibits a lower penetration
depth than the test layer step beneath it. The gold step also has a uniform (gold)
composition in its upper level and next lower level.
In accordance with another embodiment thereof, the invention provides a calibration
standard for optical profilometry step height measurements. The calibration standard has
a multilayer structure comprising an optical flat, a first layer on the surface of the optical
flat, a second layer on the first layer, a test layer on a part of the second layer, and a gold
layer on the test layer and on a part of the second layer uncovered by the test layer. The
test layer has a test layer step, and the gold layer has a gold step over the test layer step.
In accordance with another embodiment thereof, the invention provides a method of
making a reference standard for a thin film sample with one or more component thin
film layers. The method includes depositing a layer of gold over the surface of the thin
film sample.
In accordance with another embodiment thereof, the invention provides a reference
standard for a thin film sample with one or more component thin film layers. The

8. reference standard has a layer of gold that is measured by the profilometer, but is
otherwise essentially the same as the thin film sample.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other features of the invention will be described in more detail in the
following Detailed Description of the Preferred Embodiment, taken in conjunction with
the accompanying drawings wherein:
FIG. 1 is a cross-sectional view showing the multilayer structure of the first embodiment
of the invention;
FIG. 2 is a cross-sectional view showing the multilayer structure of another embodiment
of the invention;
FIG. 3 is a top view illustrating the process of preparing the multilayer thin film of the
invention; and
FIG. 4 is a cross-sectional view showing the structure of the reference standard of another
embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a first embodiment of the invention. A multilayer thin film 10, used to
calibrate an interferometer system, has an optical flat 12 preferably with a .lambda./20
smooth surface 14 of amorphous material. On the optical flat 12 is a first layer 16 which
adheres strongly to the surface 14 of the optical flat 12. On the first layer 16 there is a
second layer 20 which adheres strongly to the first layer 16. The second layer 20 has a
first part 22 and a second part 24 that are generally coplanar with each other and adjacent
to each other. On the first part 22 of the second layer 20 there is a test layer 30 which
adheres strongly to the first part 22 of the second layer 20. A gold layer 40 is located both
on the second part 24 of the second layer 20, and on the test layer 30.
The test layer 30 defines a test layer step 32, with a height of a generally known value, at
the boundary 34 of the test layer 30. The gold layer 40 defines a gold step 42 over the test
layer step 32. The gold step 42 is equivalent in height to the test layer step 32. The
interferometer system is calibrated by measuring the height of the gold step 42 several
times with the interferometer system, and then calculating the mean value, median value,
and standard deviation of the measurements.
FIG. 2 shows another embodiment of the invention. A multilayer thin film 50, which is
located on optical flat 12, comprises a first layer 60 with a thickness of about 30 nm or
less, a second layer 70 with a thickness of about 30 nm or less, a test layer 80, and a gold
layer 90 with a thickness of about 50 nm or less. The test layer 80 creates a step 82 which
is reflected in the gold layer 90 as step 92. A particular example of the multilayer thin
film 50 has a first layer 60 of titanium with a thickness of 20 nm, a second layer 70 of

9. platinum with a thickness of 20 nm, a test layer 80 of platinum with a thickness of 6 nm,
and a gold layer 90 with a thickness of 50 nm. A multilayer thin film with this
construction can act as a calibration standard for calibrating an interferometer system.
A multilayer thin film sample with the foregoing construction is formed first by
depositing a titanium and platinum bilayer on the optical flat 12. The sample is then
removed from a thin film depositing system. As shown in FIG. 3, half 110 of the sample
100 is then masked with aluminum foil 120 before the sample 100 is reloaded into the
depositing system for depositing a test layer of platinum thereon. The sample 100 is then
once again removed from the depositing system, the aluminum foil 120 is removed from
the sample, and the sample 100 is reloaded into the depositing system for depositing a
gold layer thereon.
FIG. 4 shows another embodiment of the invention, a reference standard 140 for a thin
film sample with one or more component thin film layers. The thin film sample has a
surface 150 upon which is deposited a test layer 160 that defines a step 162. The
reference standard 140 comprises a gold layer 170 on the surface 150 of the thin film
sample, which as a result of step 162 creates a step 172. Because gold has a small known
beam penetration, and the top and bottom of the steps 42 (FIG. 1), 92 (FIG. 2) and 172
(FIG. 4) are of gold, these structures can be used as accurate calibration standards for an
interferometer (profilometer) system. These structures provide accuracy for steps which
are at least 10 nanometers or less. The gold layer 170 may have a thickness no greater
than 50 nm.
While the foregoing embodiments of the present invention have been set forth in
considerable detail for the purposes of making a complete disclosure of the invention, it
should be apparent to those of skill in the art that numerous changes may be made in such
detail without departing from the spirit and principles of the invention.

10. Profilometer stylus assembly insensitive to vibration
Document Type and Number:
United States Patent 5309755
Link to this page:
http://www.freepatentsonline.com/5309755.html
Abstract:
A stylus profilometer having a counterbalanced stylus with a motion transducer using a
vane moving between parallel, spaced-apart, conductive plates which damp the motion of
the vane by means of trapped air. The vane forms an electrode with the plates so that the
combination is a pair of capacitors in a balanced bridge arrangement. Motion of the
stylus causes an unbalance of the bridge indicative of the extent of stylus motion. A lever
arm associated with the stylus has a tip influenced by a magnetic field which biases the
stylus or controls force on a surface to be measured. The entire assembly has a very low
moment of inertia to reduce the effects of vibration on the stylus and thereby increase
resolution of the device and reduce damage to the substrate.
A profilometer assembly comprising,
an elongated stylus arm and counterbalance having a first end with a hard stylus mounted
for contact with a substrate disposed below the arm and a second end, opposite the first
end having a vane for motion between two parallel plates, the stylus arm having a pivot
between the first and second ends, said parallel plates forming a stylus displacement
measurement transducer with said vane, and
a variable force member associated with the first end of the stylus arm for urging the first
end into contact with said substrate.
2. The apparatus of claim 1 wherein said variable force member comprises a coil having a
ferromagnetic core located a spaced distance from a lever connected to the first end of the
stylus arm and having a ferromagnetic tip which can be magnetically actuated from a
distance by said core.
3. The apparatus of claim 1 wherein said pivot is seated in a pivot member having a pair
of opposed ends, one end supporting the stylus arm and the opposite end supporting said
vane.
4. The apparatus of claim 1 wherein said parallel plates are disposed in air and have an
areawise extent shielding the vane from outside air.
5. A profilometer assembly comprising,
a measurement stylus mounted at the end of an arm for contact with a substrate,
a pivot member having opposed forward and rearward sides and a central region
therebetween mounted for turning on an axis defined from a relatively massive member,
the pivot member supporting said arm on the forward side and a counterweight member
on the rearward side, the counterweight including a force transducer having means for

11. signaling motion of the pivot member, and
means for adjustably biasing the forward side of the pivot member, thereby urging said
stylus into contact with the substrate, having a coil spaced from said pivot member, a
ferromagnetic core extending through the coil and a lever in magnetic communication
with the core, transmitting force induced by the coil, to the forward side of the pivot
member, the lever connected to the pivot member but spaced from said coil and core.
6. The apparatus of claim 5 wherein said arm, lever and vane have a rotational moment of
inertia about the pivot member, said moment of inertia less than 0.5 gm-cm.sup.2.
7. The apparatus of claim 5 wherein said pivot member has a rearwardly extending
paddle, said vane being connected to said paddle.
8. A profilometer assembly comprising,
a measurement stylus mounted at the end of an arm for contact with a substrate,
a pivot member having opposed forward and rearward sides and a central region
therebetween mounted for turning on an axis defined from a relatively massive member,
the pivot member supporting said arm on the forward side and a counterweight member
on the rearward side, the counterweight including a force transducer having means for
signaling motion of the pivot member, and
means for adjustably biasing the forward side of the pivot member, thereby urging said
stylus into contact with the substrate.
wherein the force transducer means comprises a pair of spaced-apart, parallel plates with
a movable vane therebetween, the vane connected to the rearward side of the pivot
member whereby motion of the stylus member is transmitted through the pivot member
to the vane.
9. The apparatus of claim 8, wherein said vane and said parallel plates form a bridge
circuit.
10. A profilometer assembly comprising,
a stylus arm for step-height measurements of a substrate,
a pivot member supporting the stylus arm,
a vane supported by the pivot member, rearwardly of the stylus arm, partially
counterbalancing the stylus arm and having a mass-radius squared product in
combination with the stylus arm not exceeding 0.5 gm-cm.sup.2, wherein the vane moves
in air between and generally parallel to two parallel plates, the air between the parallel
plates damping motion of the vane,

12. whereby the momentum of the arm is minimized in order to reduce damage to substrates.
11. The apparatus of claim 10, wherein the vane and said parallel plates define two
capacitors arranged for differential sensing of the amount of turning of said pivot thereby
sensing the deflection of said stylus arm.
12. The apparatus of claim 10 further comprising a solenoidal coil generating a magnetic
field spaced a distance from said arm and a lever having one end connected to said pivot
member and a free end having a ferromagnetic tip in communication with said magnetic
field whereby said magnetic field can bias said arm relative the substrate.
13. The apparatus of claim 10, wherein said vane moves between two fixed parallel plate
electrodes.
Description:
TECHNICAL FIELD
The invention relates to instruments for measuring profiles of surface features of a
patterned semiconductor wafer or measuring fine texture on soft substrates.
BACKGROUND ART
Profiling instruments were first developed in the 1930's for the purpose of characterizing
surfaces in terms of roughness, waviness and form. In recent years, they have been
refined for precise metrology in the measurement and production control of the thin film
artifacts which are the building blocks of semiconductor devices. As the semiconductor
industry has progressed to smaller dimensions with each new generation of product, the
need for more sensitive and precise profiling instruments has grown. As artifacts become
smaller, a smaller radius stylus must be used to fully resolve them. But a smaller radius
produces higher contact pressure and necessitates use of lower stylus force. The use of
very low stylus force renders the instrument more vulnerable to noise generation from
roughness of the measured surface and also from environmental sources of vibration. The
presence of noise in the output reduces the effective sensitivity of the instrument and
compromises the fidelity of its traces. Fidelity is also lost whenever the ratio of stylus
pressure to surface yield strength rises to the degree that plastic deformation of the
surface occurs and detail of the surface variations is obliterated. Reduction of stylus force
is the only solution to this problem.
In U.S. Pat. No. 4,103,542 Wheeler et al., assigned to the assignee of the present
invention, disclose a counterbalanced stylus arm, pivoted about a bearing, in which
stylus force may be adjusted by moving the counterbalance. Force is measured using a
linear variable differential transformer having a core associated with the stylus arm and a
coil, through which the core moves, supported independently of the arm. In U.S. Pat. No.
4,391,044 Wheeler discloses a similar stylus arm supported for linear scanning.
It is evident that operation of profilers at very low stylus force is desirable. The present

13. state of the art in commercial profilers allows operation down to 1.0 mg. of force.
However, a relatively quiet environment is necessary for good results at that force and
such conditions are not always available in the users environment. What is needed is a
reduced reaction of the stylus/sensor assembly to the vibration or shock energy pulses
which reach it from whatever source.
An object of the invention was to devise a stylus assembly for a profilometer with
improved vibration and shock insulation properties.
SUMMARY OF INVENTION
The above object has been achieved in a profilometer stylus assembly which reduces the
effects of vibration and shock energy pulses by means of a substantial decrease in the
moment of inertia of the assembly. For, as an energy pulse comes to the stylus arm
structure, it will generate an accelerating force which will tend to raise the stylus from
the sample surface either at the leading edge of the pulse or upon the rebound if the
accelerating force exceeds the set stylus force. The acceleration force developed is in
proportion to the moment of inertia of the stylus arm structure, hence its reduction allows
the use of lower stylus force.
Conventional practice in existing designs is to locate the measurement sensor, sometimes
a core working with a coil, close to the stylus on a pivoted stylus arm. A counterweight
is frequently employed on the opposite end of the arm to achieve a static balance. This
design approach assures that the sensor will precisely track the stylus motion and also
that some momentum effects are avoided when a motion pulse is introduced through the
stylus arm pivot.
Contrary to standard designs, the stylus support arm and the measurement sensor of the
present invention are in opposed positions about the pivot. A vane, supported by the
pivot, opposite the stylus, moves in air between two larger parallel capacitor plates. The
trapped air between the plates damps the motion of the vane, thereby providing clamping
of large stylus motions, while the two plates with the vane form a differential capacitor
for the measurement of motion. An important feature is that the moment of inertia about a
rotational axis can be made very small. Mass reduction at a maximum distance from the
pivot is most important.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side perspective view of a profilometer stylus assembly of the present
invention.
FIG. 2 is a front perspective view of the profilometer stylus assembly shown in FIG. 1.
FIG. 3 is a top plan view of the profilometer stylus assembly shown in FIG. 1.
FIG. 4 is a side plan view of the profilometer stylus assembly shown in FIG. 1.

14. FIG. 5 a side view of a capacitor plate used in the profilometer stylus assembly shown
in FIG. 1.
BEST MODE FOR CARRYING OUT THE INVENTION
With reference to FIGS. 1-4, a diamond tip 11 having a radius of 0.01 mm. is adhered to
an end of a slender stainless steel wire 13 which is bent at a right angle. The wire radius
is about 0.25 mm. The diamond tip is adhesively mounted to a squared-off end of the
wire, while the opposite end of the wire is inserted into a hollow aluminum arm 15 which
has a length of approximately 2 cm and a wall inside radius of approximately 0.018 cm.
The aluminum arm is sufficiently rigid that it will not bend when sensing step heights, yet
sufficiently low mass that its moment of inertia can be kept low. The overall mass of the
arm, wire and diamond tip should not exceed approximately 0.05 grams. Arm 15 fits into
a groove 17 in pivot member 19. Washer 21 holds the arm in place in the groove 17,
while a tiny screw 23 holds the washer in place against the wall of the pivot member 19.
Support beam 25 has a downwardly extending column 27 to which a flexural pivot 29 is
mounted, connecting the pivot member 19 to the column 27. In this manner, the
aluminum arm 15 has a center of rotation about the flexural pivot 29. The flexural pivot
29 has enough torsion to lightly hold the stylus tip 11 downwardly against a surface to be
measured. The entire mass on the stylus side of the pivot should not exceed 0.50 grams,
including a lever described below.
A frame 31 may be connected to a tilt compensation or leveling mechanism as described
in the prior patents to Wheeler. The underside of frame 31 supports a connector block 33
which acts as an elevational adjustment for a pair of spaced apart parallel capacitor plates
35 and 37. The spacing between the plates is approximately 0.7 mm., with an air gap
between the plates.
FIG. 5 shows the detail of a single capacitor plate. Such plate features a planar ceramic
member 61 having a pair of conductive films which are silkscreened and then fired on the
ceramic member to form a capacitor plate. The two plates are identical and so only one is
shown. A conductive metal film 63 is shown extending through a via hole 65, in the
ceramic member. The upper surface of the drawing represents the side of the plate facing
the movable vane 41 in FIG. 1. The purpose of the via hole 65 is to provide electrical
connection to a thin wire which is soldered on an outer surface solder pad and carries the
signal from the capacitor plate to associated electronics. Wire 39 in FIG. 4 is such a wire.
A second conductive metal layer 71 is in insulative relationship with respect to metal
layer 63, but is also deposited on the ceramic member 61. The layer is plated through a
second via 73 and has a bonding ring 75 on the backside of the capacitor plate. Layer 71
serves to terminate the shield of the wire which is terminated in via 65. The shield
reduces electrical noise pickup.
Returning to FIGS. 1-4, a small insulative spacer, not shown, separates plate 35 from
plate 37 and a screw fastens the two plates to frame 31. The area extent of the plates
should be large enough to shield the vane from outside air, so that the vane experiences

15. resistance to motion due to compression of air momentarily trapped between the closely
spaced plates. A pair of electrical leads 39 is connected to the parallel plates, one lead to
each plate. Between the parallel plates, a low mass of electrically conductive vane 41 is
spaced, forming a capacitor with respect to each of the parallel plates 35 and 37. The
range of motion of the vane, indicated by arrows A in FIG. 4, is plus or minus 0.16 mm.
Moreover, vane 41, being connected to the pivot member 19, damps pivoting motion as
the vane attempts to compress air between the parallel plates. This damping motion of the
vane serves to isolate vibration and shock which may be transmitted into arm 15.
Vane 41 is connected to a paddle 43 which is the rearward extension of pivot member 19,
opposite arm 15, serving to counterbalance the arm. The total mass of the vane, paddle
and pivot member on the vane side of the pivot should not exceed about 0.6 g. The vane
41 is grounded so that a differential pair of capacitors may be formed with respect to
parallel plates 35 and 37 with their respective electrical leads 39. Such a pair of
capacitors may be arranged in a balanced bridge configuration. Movement of the vane
between plates 35 and 37 upsets the balance of the bridge, with the change of capacitance
indicative of stylus tip motion.
An electrical solenoidal coil 51 has a central ferromagnetic core 53 which becomes
magnetized on application of current to the coil 51 by means of wires 55. The magnetized
central ferromagnetic core 53 attracts a ferromagnetic tip 57 of a lever 59 having an end
opposite the ferromagnetic tip which is affixed to the pivot member 19. By applying
current to the wires 55 and magnetizing the core 53, magnetic force is exerted on the
lever 59 causing a bias in the form of a rotation, indicated by the arrow B in FIG. 4. The
lever 59 should be light weight, yet stiff so that the lever will not bend on the application
of magnetic force.
In operation, the stylus tip 11 scans a surface to be measured, such as a patterned
semiconductor wafer. Scanning may be achieved either by moving the frame 31 with
respect to a fixed wafer position or alternatively moving the wafer, on an X-Y wafer
stage with the position of the stylus fixed, or a combination of the two motions. In the
latter instance, the stylus arm may be moved linearly in the X direction while the wafer is
advanced in the Y direction after each lengthwise X direction scan. The stylus tip 11 is
maintained in contact with the surface of the wafer by an appropriate bias applied through
the coil 51 and the core 53 into the lever 59. The bias should be great enough to maintain
contact, but yet not damage the surface being measured. Deflections of the tip 11 are
caused by topological variances in the surface being measured and these are translated
rearwardly through the pivot member 19 to the vane 41, but which resists undesirable
large amplitude motion due to vibration because of the air displacement between the
parallel plates 35 and 37. However, as the air is compressed and displaced, the vane 41
moves slightly causing a signal in electrical leads 39 reflecting a change in an electrical
bridge circuit connected to these wires. At the end of a scan, the tip 11 is raised to protect
it from damage in the event that a wafer is changed.
In building arm 15, wire 13 and tip 11, it is important to maintain the moment of inertia
as small as possible. The mass-radius squared product should not exceed about 0.5 g-

16. cm.sup.2 and we have achieved a mass-radius squared product of 0.42 g-cm.sup.2. The
radius is measured with respect to the center of the spring pivot 29 to the furthest radial
extent of the steel wire 13. A similar moment of inertia is calculated with respect to the
vane 41 and the lever 59. The sum of the moments is termed the moment of inertia for the
entire stylus arm. By maintaining a low moment of inertia, the stylus arm is less sensitive
to vibration and greater resolution in profile measurements of thin films, and the like,
may be achieved.
Profilometers
Veeco Dektak Stylus Profilometer
The stylus profilometer uses a diamond tipped stylus to
scan across the sample surface and measures the surface
topography of thin and thick films. The vertical
movements of the stylus is measured and recorded
simultaneously during the scanning, which reveals the
topographical structure of the surface. The instrument has
vertical resolution in nanometers and horizontal resolution
as small as twenty nanometers and measures the film
thicknesses from 5 nm and over 500 µm.
Tài liệu tham khảo
Possibilities and limitations of the stylus method for thin film thickness measurements
Thin Solid Films, Volume 21, Issue 2, April 1974, Pages 237-243